Net-shape or near net-shape powder isostatic pressing process

ABSTRACT

A method of producing a net or near net-shape component from metal powder comprises producing an insert of accurate dimensions corresponding to the dimensions of a bore to be created in the finished component, the bore having a length of at least 750 mm, supporting the insert within a mould cavity, filling the mould cavity with metal powder, subjecting the powder to isostatic pressing, and subsequently removing the material of the insert. The mould can be an independent mould that is removed after an initial step to bind the powder together into a pre-form, and the pre-form is then encapsulated in a suitable containment, such as a canister or a sprayed coating. The insert can be a metallic insert of a material, such as copper, that is subsequently removable by chemical etching. The insert can be coated with a material that is amenable to removal by etching, and to enable the insert to be extracted. A metallic insert can be coated with a material that provides a diffusion barrier to prevent the material of the insert from diffusing by atomic diffusion into the powder being consolidated during HIPing.

The invention relates to net-shape or near net-shape powder isostaticpressing processes, as applied to metallic and/or cermet/MMC (metalmatrix composites) powder.

The invention is concerned particularly, but not exclusively, with theproduction of a bore of substantial length, typically longer than 750mm, in a component of hard wear-resistant material.

Such components can be made by Hot Isostatic Pressing (HIPing) but it isextremely difficult to produce bores in the formed components bymachining. With difficulty, straight bores of small length such as 10 mmcan be machined.

We consider that it would be of advantage in certain circumstances toprovide a bore of accurate dimensions extending lengthwise through acomponent of length approximately 2 m, the component desirably beingproduced from a powder by a hot isostatic pressing process so as toprovide hard wearing properties.

According to one aspect of the invention a method of producing a net ornear net-shape component from metal powder comprises producing an insertof accurate dimensions corresponding to the dimensions of a bore to becreated in the finished component, the bore having a length of at least750 mm, supporting the insert within a mould cavity, filling the mouldcavity with metal powder, subjecting the powder to isostatic pressing,and subsequently removing the material of the insert.

As is well known, the mould may be an independent mould that is removedafter an initial step to bind the powder together into a pre-form, andthe pre-form is then encapsulated in a suitable containment which may bea canister or a sprayed coating, or a canister of suitable internalshape may be used as the mould, and the canister itself is evacuatedprior to HIPing

Preferably the insert is supported in position in the mould cavity by aplurality of formers of a material that is compatible with the finallyconsolidated powder.

The insert may be a metallic insert of a material that is subsequentlyremovable by chemical etching, preferably copper. The chemical etchingmay be assisted by electrolytic reaction.

In suitable cases the insert need only be coated with a material thatcan subsequently be removed by etching, in order to release the insert,which can then be extracted.

Preferably the metallic insert is coated with a suitable material thatprovides a diffusion barrier to prevent the material of the insert fromdiffusing by atomic diffusion into the powder being consolidated duringHIPing.

The invention can enable a helical bore to be provided in a component.

Such a helical bore could be used for various purposes, such as toconvey a fluid and/or to accommodate an electrical or fibre-optic cableto provide sensor or control system communications for example.

In one preferred embodiment a copper rod, of a diameter in the range of6 to 10 mm for example and of length greater than 2 m, is first bentinto a helix of the required dimensions and this is then held inposition in a powder containment prior to filling the containment withpowder. The containment enclosing the powder, rod and former, is thenconsolidated by solid state diffusion using the HIPing method.

The diffusion barrier may be Al₂O₃ applied by vapour phase deposition orby high velocity spraying. Alternatively, the diffusion barrier may becreated by applying boron nitride as an aqueous solution by spraying.

In a second embodiment a preformed metal tube, of 6 mm to 10 mm diameterfor example, is filled with ceramic particles and is bent to a helicalshape and placed within the powder containment prior to filling thecontainment with powder. The tube is held in position with formerscompatible with the finally consolidated powder. The entire containmentencompassing the metallic and/or cermet/MMC powder is then consolidatedby solid state diffusion using the HIPing method.

During consolidation the metal tube may become totally diffusion bondedinto the consolidated component but the ceramic particles will remain inthe pre-process particle form and thereby can be removed mechanicallyvia vibration techniques to leave a clean hole through the component.

EXAMPLE

The invention can be used to provide one or more holes in one or morehelical lobes provided internally of the stator body of a helicoidalpositive displacement pump, the stator body having a length of as muchas 2 m or more. Such stator bodies can be used to form the radiallyouter part of a linear motor and/or mud pump used in down-hole drilling.The hole or holes can be positioned to follow the core of a helicalflute, which may have a pitch of about 1 m and a radius of 50 mm aboutthe body axis. The helical lobes are defined by helical grooves in amandrel that is positioned in the mould during pressing of the statorbody.

1. A method of producing a net or near net-shape component from metalpowder comprising producing an insert of accurate dimensionscorresponding to the dimensions of a bore to be created in the finishedcomponent, the bore having a length of at least 750 mm, supporting theinsert within a mould cavity, filling the mould cavity with metalpowder, subjecting the powder to isostatic pressing, and subsequentlyremoving the material of the insert.
 2. The method of claim 1 in whichthe mould is an independent mould that is removed after an initial stepto bind the powder together into a pre-form, and the pre-form is thenencapsulated in a suitable containment.
 3. The method of claim 2 inwhich the containment is a canister.
 4. The method of claim 2 in whichthe containment is a sprayed coating.
 5. The method of claim 1 in whichthe insert is supported in position in the mould cavity by a pluralityof formers of a material that is compatible with the finallyconsolidated powder.
 6. The method of claim 1 in which the insert is ametallic insert of a material that is subsequently removable by chemicaletching.
 7. The method of claim 6 in which the insert comprises copper.8. The method of claim 7 in which the chemical etching is assisted byelectrolytic reaction.
 9. The method of claim 1 in which the insert iscoated with a material that is amenable to removal by etching, andcomprising the steps of releasing the insert by etching the coating, andthen extracting the insert.
 10. The method of claim 6 in which themetallic insert is coated with a material that provides a diffusionbarrier to prevent the material of the insert from diffusing by atomicdiffusion into the powder being consolidated during HIPing.
 11. Themethod of claim 10 in which the diffusion barrier comprises Al₂O₃applied by vapour phase deposition.
 12. The method of claim 10 in whichthe diffusion barrier comprises Al₂O₃ applied by high velocity spraying.13. The method of claim 10 in which the diffusion barrier is created byapplying boron nitride as an aqueous solution by spraying.
 14. Themethod of claim 1 in which the insert is produced by taking a copperrod, of a diameter in the range of 6 to 10 mm and of length greater than2 m, bending the copper rod into a helix of the required dimensions, andthen holding the helical rod in position in a powder containment priorto filling the containment with powder, the containment enclosing thepowder, rod and former, and then consolidating the powder by solid statediffusion using a HIPing method.
 15. The method of claim 1 in which theinsert is produced by taking a preformed metal tube, of 6 mm to 10 mmdiameter, filling the tube with ceramic particles, and bending thefilled tube to a helical shape, placing the helical filled tube withinthe powder containment prior to filling the containment with powder,holding the tube in position with formers compatible with the finallyconsolidated powder, providing a containment encompassing the metallicand/or cermet/MMC powder, and then consolidating the contained materialby solid state diffusion using a HIPing method.
 16. The method of claim15 comprising removing the ceramic particles mechanically by a vibrationtechnique to leave a clean hole through the finished component.
 17. Anet or near net-shape component produced by the method of claim 1.